The semiconductor Integrated Circuit (IC) industry has experienced rapid growth. In the course of IC evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometry size (i.e., the smallest component (or line) that can be created using a fabrication process) has decreased. This scaling down process generally provides benefits by increasing production efficiency and lowering associated costs. However, such scaling down has also been accompanied by increased complexity in design and manufacturing of devices incorporating these ICs. Parallel advances in manufacturing have allowed increasingly complex designs to be fabricated with precision and reliability.
For example, some advances compensate for optical effects and processing imperfections that occur near the limits of lithography. In many examples, ICs features are defined and formed on a semiconductor substrate using a set of photolithographic masks. The masks have patterns formed by transmissive and/or reflective regions. During a photolithographic exposure, radiation such as ultraviolet light passes through or reflects off the mask before striking a photoresist coating on the substrate. The mask transfers the pattern onto the photoresist, which is then selectively removed to reveal the pattern. The substrate then undergoes processing steps that take advantage of the shape of the remaining photoresist to create circuit features on the substrate. When the processing steps are complete, another photoresist is applied and substrate is exposed using the next mask. In this way, the features are layered to produce the final circuit.
However, the patterns formed on the substrate may vary from the patterns of the mask. For example, optical effects including diffraction, fringing, and interference may affect where radiation falls on the workpiece. Likewise, properties of the masks, the lithographic system, and/or the workpiece may determine which portions of the photoresist are exposed. Variability in processing steps such as photoresist developing, etching, deposition, implantation, etc. may also affect the shape of the final pattern. If not accounted for, these effects may cause variances such as corner rounding, edge errors, necking, bridging, and incomplete features.